Optical electronic displays are widely found in handheld devices such as cellular phones, MP3 players and other portable electronic devices. The inorganic glass front panels on these devices are usually clear and fragile. A protective layer of highly optical transmission films/sheets is generally laminated on top of the glass panel displays. There is a need to further improve the light transmittance of the protective layer in terms of higher light efficiency/brightness and a low haze level of <2%, and even <1% in a photopic region. Additionally, any protective layer should be easy to apply and have good chemical resistance, scratch resistance and dirt-shedding performance.
Photovoltaic (PV) modules generally have low iron tempered glass front panels, due to high light transmittance (>90.5%) and excellent weathering performance. However, the glass front panels are usually heavy (bulk desity ˜2.5 g/cm3) and fragile. A solution is to laminate a polymeric film onto a thinner glass substrate to improve the performance in terms of light efficiency, dirt shedding and impact resistance, and even to use plastic sheets to replace the glass panels.
Acrylic sheet, such as PLEXIGLAS polymethyl methacrylate (PMMA) sheet (Arkema Inc.) is an optically clear plastic product developed at Altuglas International with superior optical clarity and excellent weathering performance as well as light weight (bulk density=1.2 g/cm3). The optical PMMA sheets are considered a good candidate substrate to replace the glass panels for both PV module and electronic display applications.
Polyvinylidene fluoride (PVDF) films have been laminated (U.S. Pat. No. 4,226,904) and extruded (U.S. Pat. No. 4,317,860) onto PMMA sheets to improve the chemical resistance. Multi-layer films having a PVDF outerlayer and a PMMA inner layer have been laminated/adhered onto differenent substrates, including glass and plastics (U.S. Pat. Nos. 5,132,164; 6,811,859). Multi-layer PVDF/PMMA films have been used for PV protective coatings (U.S. Pat. No. 7,267,865).
“Moth-eye” anti-reflective coatings, having a particulate structure have been applied to both inorganic and organic substrates by an etching process. The anti-reflective nano moth-eye structures have been developed at a small scale based on low pressure plasma or ion etching surface treatment (with irregular 3D nano moth-eye structure DE 10241708.2) or complicated laser holographic/lithographic fabrication technologies on master structures (with periodic 3D niotheye structures at the size of ˜250 nm). Physical application of a nanostructure surface patern by stamping or the use of a matte roller in a sheet formation manufacturing process. Moth-eye anti-reflective coatigs are not currently produced based on wet chemistry.
PVDF coatings have been applied to thermoplastic substrates in both flexible and non-flexible PV front sheet (WO 08/019229; US 60/989,501). These coatings tend to be thick (>5 microms), and are formed from polymers having a large (>˜300 nm) particle_size. The current PVDF and other fluorpolymer coating technologies tend to be hazy which is undesirable for portible electronic device screens.
Surprisingly it has been found that optically clear coatings, and especially fluoropolymer coatings, can be applied to a substrate in a process resulting in a particulate or “moth eye”-type nano-structure. This nano-structured coating provides improved_chemical and scratch resistance, yet also gives improved optical light transmittance and very low haze by reducing the light reflection. The nano-structure is preferably cross-linked for stability of the structure.